Boletín de aludes

South Rockies

Mar 4 – 5, 2021Avalanche Canada
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Archivado · caducó 6 years ago

Peligro de aludes

Sat
Sun
Alta montaña
4 · Fuerte
Límite del bosque
4 · Fuerte
Bajo el límite
4 · Fuerte
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Lo esencial

This is the first significant warm-up in March and we expect this to complicate current avalanche conditions. The danger may be CONDSIDERABLE in the morning but on the rise for the afternoon. Check out the new Forecaster Blog on warming and the effects on our complex snowpack 

Problemas de aludes

  • Cornices

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely - Very Likely
    Tamaño
    1–2

    Large looming cornices exist along ridgelines and require a wide berth from above and below. The likelihood of them becoming weak and failing is HIGH with warming and solar radiation. They have the potential to trigger slab avalanches from slopes below. 

    West to southwest wind has formed isolated wind slabs on leeward slopes. These could be triggered by the weight of a skier or rider, especially on east-northeast aspects. 

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2.5

    Two layers of concern exist and have been reactive over the past couple of days. The upper layer being buried mid-February down 30-60 cm and has recently failed primarily on a sugary facet interface and the deeper layer of concern is found down 60-100 cm and consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine. 

  • Loose Wet

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Very Likely
    Tamaño
    1–2

    Wet loose avalanches are likely as the sun pokes out and freezing levels rise. Be observant as you travel, and look for signs of warming and snowpack instability. Snowballing, moist snow, and the most obvious is natural avalanche activity. Back off slopes and adjust your trip plan when things are heating up.

Confidence

Moderate - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather. A small change in the upper snowpack could dramatically change avalanche conditions.

Weather Forecast

It's a hot and sunny forecast with generally light to moderate south wind. Thursday through Saturday will see mostly sunny skies with patches of cloud cover. Freezing levels are forecast to rise above 2000 m driving alpine temperatures above freezing. Sunday should bring cloud cover and a cooling trend. 

Avalanche Summary

No new avalanches reported on Wednesday.

Sun and warming is our primary concern over the next few days. Large looming cornices may weaken and fail, triggering slabs on the slopes below. Loose-wet avalanches will likely be seen from solar aspects first and then possibly all aspects. The persistent slab above the weak layers may stiffen and consolidate further, failing as a natural avalanche or becoming more sensitive to skier and rider triggers.  

Pockets of wind slab may be reactive on northeast-east aspects at upper elavtions. 

Snowpack Summary

Upper elevations are highly wind-affected and scouring down to rocks or crusts can be seen on west to southwest aspects. On leeward (northeast-east) slopes, stiff pockets of wind-slab has formed at treeline and in the alpine.

40 to 60 cm (in some places up to a meter) of snow now sits above sugary faceted snow that formed mid-February. Recent snowpack testing shows a relatively easy to moderate failure on the mid-Feb layer which propagated across the whole column (ECTP 13 down 40 cm). This test was on a south-facing slope at treeline and shows the sensitivity of this weak layer. Deeper in the snowpack (60 to 100 cm deep) is another weak layer that was buried at the end of January. This layer consists of surface hoar, faceted grains, and/or a hard melt-freeze crust. MIN reports prove these layers remain easily triggered by people. 

Weak faceted grains and a decomposing melt-freeze crust can be found near the base of the snowpack. 

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.

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